NEET-PG 2012 Practice Questions

Q: Which is the primary segment of the liver drained by the right hepatic vein?

VII. ***VII*** - The **right hepatic vein** drains the **posterior segment** of the right lobe, which includes segments **VI and VII**. Segment VII is particularly well-drained by this vein. [3] - Understanding hepatic venous drainage is crucial for **surgical planning** and interpreting imaging studies of the liver. [4] *I* - Segment I, the **caudate lobe**, is unique in its venous drainage, often by small veins directly into the **inferior vena cava (IVC)** or occasionally into the left and middle hepatic veins. [1] - It has a separate blood supply and drainage which differentiates it from other segments. [4] *II* - Segment II is part of the **left lateral segment** and is primarily drained by the **left hepatic vein**. - The left hepatic vein typically drains segments II and III. [2] *IV* - Segment IV, or the **quadrate lobe**, is primarily drained by the **middle hepatic vein**. - The middle hepatic vein also drains segment VIII and the anterior aspect of segment V.

Q: Which bone has the maximum anatomical contribution to the floor of the orbit?

Maxillary. ***Maxillary*** - The **maxilla** contributes the most significantly to the **orbital floor**, forming approximately **75%** of its surface area. - The orbital plate of the maxilla is a thin, triangular bone that also forms the roof of the **maxillary sinus**. *Zygomatic* - The **zygomatic bone** forms the **lateral wall** and the **lateral portion** of the **orbital floor**. - Its contribution to the overall floor is less extensive than that of the maxilla (approximately 20-25%). *Sphenoid* - The **sphenoid bone** does **NOT** contribute to the **orbital floor** at all. - It forms parts of the **posterior wall** and **lateral wall** (via greater and lesser wings) of the orbit, but has no anatomical contribution to the floor. *Palatine* - The **palatine bone** (via its orbital process) contributes a very small, **posterior-most part** of the **orbital floor**. - Its contribution is minimal (less than 5%) compared to the maxilla and zygomatic bone.

Q: Which of the following statements about protein denaturation is correct?

The primary structure of the protein is unaffected.. ***The primary structure of the protein is unaffected.*** - Denaturation refers to the disruption of a protein's **secondary, tertiary, and quaternary structures**, while the **covalent peptide bonds** that form the primary structure remain intact. - The sequence of amino acids, which defines the primary structure, is not typically altered by denaturing agents such as heat, pH changes, or chemicals. *Biological properties are retained after denaturation.* - Denaturation typically leads to the **loss of a protein's specific three-dimensional shape**, which is essential for its biological function. - Therefore, the biological properties and **activity of the protein are usually lost** or significantly impaired upon denaturation. *Denaturation is always irreversible.* - While many cases of denaturation are irreversible (e.g., cooking an egg), some proteins can **renature** if the denaturing conditions are removed, restoring their original structure and function. - This reversibility depends on the **severity and duration of the denaturing agent**, as well as the protein's inherent stability. *Denaturation never results in proteins becoming insoluble.* - Denaturation often exposes **hydrophobic regions** of a protein that were previously buried within its folded structure, leading to aggregation and **precipitation**, thereby making the protein insoluble. - This insolubility is a common consequence of denaturation, particularly with significant structural disruption.

Q: Which of the following is not a precursor in the synthesis of pyrimidines?

Thymidine. ***Thymidine*** - **Thymidine** is a *nucleoside* consisting of deoxyribose and thymine. It is a *product* and a component of DNA, not a precursor in the *de novo synthesis* of pyrimidine bases. - While it can be incorporated into DNA via the *salvage pathway*, it does not serve as an initial building block for the pyrimidine ring itself. *Glutamine* - **Glutamine** provides the **nitrogen atoms** crucial for the formation of the pyrimidine ring, specifically N3 in the pyrimidine base. - It is a key donor of *amino groups* in various anabolic pathways, including nucleotide synthesis. *Carbon dioxide (CO2)* - **Carbon dioxide (CO2)** contributes one of the carbon atoms (C2) to the pyrimidine ring. - It combines with **ammonia** (derived from glutamine) to form **carbamoyl phosphate**, an essential intermediate. *Aspartic acid* - **Aspartic acid** provides four atoms (N1, C4, C5, C6) of the pyrimidine ring. - Its carbon skeleton and amino group are directly incorporated into the pyrimidine structure during the *de novo synthesis* pathway.

Q: What is the rate-controlling enzyme of fatty acid synthesis?

Acetyl-CoA carboxylase. ***Acetyl-CoA carboxylase*** - **Acetyl-CoA carboxylase (ACC)** catalyzes the committed step in fatty acid synthesis, converting **acetyl-CoA** to **malonyl-CoA**. - This enzyme is subject to both allosteric regulation (e.g., activation by **citrate** and inhibition by **long-chain fatty acyl-CoA**) and hormonal regulation (e.g., phosphorylation by glucagon and dephosphorylation by insulin). *Thioesterase* - **Thioesterase** is the enzyme responsible for releasing the completed fatty acid chain from the **fatty acid synthase complex**. - While essential for the termination of synthesis, it does not regulate the initiation or overall rate of the pathway. *Transacetylase* - **Transacetylase** (specifically, acetyl-CoA-ACP transacetylase and malonyl-CoA-ACP transacetylase) is involved in transferring acetyl and malonyl groups to the **acyl carrier protein (ACP)** within the fatty acid synthesis complex. - This is an intermediary step, but not the primary **rate-controlling** or committed step. *Ketoacyl synthase* - **Ketoacyl synthase (or β-ketoacyl-ACP synthase)** is responsible for condensing the growing acyl chain with malonyl-ACP, leading to the formation of a **β-ketoacyl-ACP**. - This is a crucial chain elongation step within the fatty acid synthase complex, but not the enzyme that controls the overall commitment to fatty acid synthesis.

Q: What coenzyme is required by gulonate dehydrogenase for its activity?

NAD. ***NAD*** - **Gulonate dehydrogenase** is an enzyme involved in the **uronic acid pathway**, specifically in the conversion of **L-gulonate to D-xylulose**. - This reaction is an **NAD-dependent oxidation**, meaning **NAD** acts as the electron acceptor, being reduced to **NADH**. *NADP* - **NADP** (nicotinamide adenine dinucleotide phosphate) is primarily involved in **anabolic pathways** like **fatty acid synthesis** and the **pentose phosphate pathway**, often in reduction reactions where it is converted to **NADPH**. - While structurally similar to NAD, it is generally not the direct coenzyme for gulonate dehydrogenase. *FAD* - **FAD** (flavin adenine dinucleotide) is a coenzyme derived from **riboflavin** (vitamin B2) and is typically involved in **redox reactions** where it repeatedly accepts and donates electrons, often in dehydrogenase reactions involving **carbon-carbon double bonds**. - Enzymes like **succinate dehydrogenase** (in the citric acid cycle) or acyl-CoA dehydrogenase (in fatty acid oxidation) utilize FAD, but not gulonate dehydrogenase. *FMN* - **FMN** (flavin mononucleotide) is another coenzyme derived from **riboflavin** and serves as a prosthetic group in various **flavoproteins**, often facilitating **single-electron transfers**. - It is frequently found in complexes like **NADH dehydrogenase** (Complex I of the electron transport chain) but is not the required coenzyme for gulonate dehydrogenase activity.

Q: What is the normal range for the CSF/plasma glucose ratio?

0.6 - 0.8. ***Correct: 0.6 - 0.8*** - This ratio indicates that cerebrospinal fluid (CSF) glucose concentration is typically 60-80% of plasma glucose concentration - This range is crucial for identifying metabolic or infectious pathologies affecting the central nervous system - Normal CSF glucose is approximately 50-80 mg/dL when plasma glucose is 70-120 mg/dL *Incorrect: 0.2 - 0.4* - A ratio in this range indicates significantly low CSF glucose, suggesting conditions like bacterial meningitis or hypoglycorrhachia - This is well below the normal physiological proportion of glucose in the CSF relative to plasma - Seen in bacterial/tuberculous meningitis, fungal infections, or malignancy *Incorrect: 1.0 - 1.2* - A CSF/plasma glucose ratio close to or above 1.0 would imply that CSF glucose levels are equal to or higher than plasma levels, which is physiologically impossible under normal conditions - Glucose transport into the CSF is regulated by GLUT-1 transporters and typically results in lower concentrations than in plasma - The blood-brain barrier maintains this gradient *Incorrect: 1.2 - 1.6* - This range is even more exaggerated and physiologically impossible, as CSF glucose cannot exceed plasma glucose in a healthy individual - Such a high ratio would contradict the mechanisms of glucose transport across the blood-brain barrier - Would suggest laboratory error if observed

Q: What is the process by which water moves from the extracellular space to the intracellular space?

Osmosis. ***Osmosis*** - **Osmosis** is the movement of water across a **semipermeable membrane** from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration). - In the context of fluid shifts, if the **extracellular fluid** becomes hypotonic relative to the **intracellular fluid**, water will move into the cells to equalize the solute concentration. *Diffusion* - **Diffusion** refers to the net movement of particles from an area of higher concentration to an area of lower concentration, down their **concentration gradient**. - While water molecules can diffuse, **osmosis** specifically describes the net movement of water across a membrane due to **solute concentration differences**, which is the precise mechanism for water moving between fluid compartments. *Filtration* - **Filtration** is the process by which water and solutes move across a membrane due to a **pressure gradient**, typically a **hydrostatic pressure gradient**. - This process is crucial in the kidneys for forming filtrate, but it is not the primary mechanism for water movement between the intra- and extracellular spaces based on solute concentration. *Active transport* - **Active transport** involves the movement of molecules across a membrane against their **concentration gradient**, requiring **energy expenditure** (e.g., ATP). - Water movement between fluid compartments is generally a passive process, relying on **osmotic gradients** rather than direct energy input to pump water molecules.

Q: IVC filter is used in the following situations except -

As primary treatment for acute DVT. ***As primary treatment for acute DVT*** - The **primary treatment** for **acute deep vein thrombosis (DVT)** is **anticoagulation therapy** (heparin, warfarin, or DOACs) to prevent clot propagation and embolization. - An **IVC filter** is **NOT primary therapy**—it is reserved for specific situations and does not treat the underlying thrombosis. - **Indications for IVC filter include:** - Absolute **contraindication to anticoagulation** (active bleeding, recent hemorrhagic stroke) - **Recurrent PE despite adequate anticoagulation** - Complications from anticoagulation therapy - Therefore, using IVC filter as primary treatment for acute DVT is **incorrect and not indicated**. *Negligible size of emboli* - While IVC filters trap **large emboli**, the concept of "negligible size emboli" is not a standard clinical consideration for filter placement. - IVC filters are indicated based on **risk of PE** and **contraindications to anticoagulation**, not based on emboli size assessment. *To reduce symptoms* - **IVC filters** do not reduce symptoms of DVT such as pain, swelling, or discomfort. - They function as a **mechanical barrier** to prevent emboli from reaching pulmonary circulation. - Symptom management requires anticoagulation, compression therapy, and leg elevation. *To prevent progress of native blood vessel disease* - IVC filters do not influence progression of underlying **vascular disease** such as atherosclerosis or chronic venous insufficiency. - Their sole function is **mechanical prevention of PE**, not disease modification.

Question 1

Which is the primary segment of the liver drained by the right hepatic vein?

Accepted Answer

VII

Answer

I

Answer

II

Answer

IV

Question 2

Which statement accurately describes a characteristic of synovial joints?

Accepted Answer

Hyaline cartilage covers the articular surfaces of synovial joints.

Answer

The metacarpo-phalangeal joint is a condyloid joint.

Answer

Cartilage can sometimes divide the joint into two cavities.

Answer

Stability is inversely proportional to mobility in synovial joints.

Question 3

Which bone has the maximum anatomical contribution to the floor of the orbit?

Accepted Answer

Maxillary

Answer

Zygomatic

Answer

Sphenoid

Answer

Palatine

Question 4

Which of the following statements about protein denaturation is correct?

Accepted Answer

The primary structure of the protein is unaffected.

Answer

Biological properties are retained after denaturation.

Answer

Denaturation is always irreversible.

Answer

Denaturation never results in proteins becoming insoluble.

Question 5

Which of the following is not a precursor in the synthesis of pyrimidines?

Accepted Answer

Thymidine

Answer

Glutamine

Answer

Carbon dioxide (CO2)

Answer

Aspartic acid

Question 6

What is the rate-controlling enzyme of fatty acid synthesis?

Accepted Answer

Acetyl-CoA carboxylase

Answer

Thioesterase

Answer

Transacetylase

Answer

Ketoacyl synthase

Question 7

What coenzyme is required by gulonate dehydrogenase for its activity?

Accepted Answer

NAD

Answer

FAD

Answer

FMN

Answer

NADP

Question 8

What is the normal range for the CSF/plasma glucose ratio?

Accepted Answer

0.6 - 0.8

Answer

1.2 - 1.6

Answer

0.2 - 0.4

Answer

1.0 - 1.2

Question 9

What is the process by which water moves from the extracellular space to the intracellular space?

Accepted Answer

Osmosis

Answer

Diffusion

Answer

Filtration

Answer

Active transport

Question 10

IVC filter is used in the following situations except -

Accepted Answer

As primary treatment for acute DVT

Answer

To reduce symptoms

Answer

Negligible size of emboli

Answer

To prevent progress of native blood vessel disease

NEET-PG 2012

Anatomy

Biochemistry

Physiology

Surgery